Comparison of Methods for the Mitigation of Line Disturbances Due to PWM AC Drives

Abstract

Several methods are used to reduce the line current harmonics created by PWM AC drives, and by doing so, also reduce the voltage distortion at the secondary terminals of the supply transformer. However, each method also impacts the power distribution system in a different way, and has an impact on the operation of the drive itself. This paper will review and compare the effects that harmonic mitigating methods have on the line supply and on the drive. The comparisons are supported by computer simulations of drive systems and verified by extensive tests that were conducted in the lab.

Energy Reductions in the Pulp-and-Paper Industry by Upgrading Conventional Pumping Systems through the Installation of VFDs – A Case Study

“…However, in exceptional conditions, when most direct powered motors on the same bus are turned off, and thus when the relative VFD driven power increases, a THD value as high as 10% can be present. This means that harmonics filters must be used if problems such as transformer excessive heating are observed [15]. There was no observable transformer temperature increase, as it was measured between 45ºC and 49ºC, for an external July temperature between 24ºC and 29ºC, both before and after VFD installation.…”

“…• Increase in parasitic currents in cables and ground circuits, that may affect communication systems and develop voltage spikes in the motor windings; • Depending on load, may increase temperature on cables and motor -not tested for the cables here; • Possible increased costs with additional filtering on the Drive, as well as costs with motors and cables with improved characteristics for VFD applications; • Worsening of the THD on the power buses -studying alternatives [13,15]; • The installation of VFDs increases the likelihood of raising the system downtime and requires well-trained maintenance teams. However, very important advantages outweigh the listed disadvantages and are reviewed here:…”

Electrical System Design of Local Generator Applications Involving Adjustable-Speed Drives

“…Both LV and MV 18-pulse techniques and AFEs also improve the power factor to ∼0.99, which can allow additional loading on the generator to be added. Passive or active filter units could also be applied to contain harmonic currents to Node 2, but the application of these is beyond the scope of this paper [9].…”